1. Field of the Invention
This invention relates to protein complexes with a saponin or a bile acid which are useful as emulsifiers for foods, pharmaceuticals, cosmetics and the like or bread dough improvers.
2. Brief Description of the Background Art
Proteins have an amphiphilic structure equipped with both hydrophilic and hydrophobic regions in one molecule and have an emulsifying action. In addition, proteins are not only of high nutritive value as foods but also have functional properties such as gel forming property and water retaining property. Therefore, they are distinguished from low molecular weight surfactants. Particularly, proteins, such as casein, gelatin and albumin, have conventionally been used as an emulsifier for foods or pharmaceuticals.
However, generally, proteins have a high molecular weight and a complex molecular structure. Therefore, since they are different from low molecular weight surfactants, they cannot be oriented easily on an interface.
As a process for imparting an emulsifying property to proteins by changing their structure to cause orientation on an interface, known are a process for introducing a fatty acid into a protein [J. Agric. Food Chem., 30:481-486 (1982)], a process for introducing lecithin into a protein (JP-B-1-50720, JP-A-5-236896 and JP-B-6-18626; the terms "JP-A" and "JP-B" as used herein mean an "examined Japanese patent publication" and an "unexamined published Japanese patent application", respectively), a process for introducing lysolecithin into a protein (JP-A-6-54650), a process for introducing a polysaccharide into a protein [J. Agric. Food Chem., 41:540-543 (1993)], a process for producing mixture of a partially decomposed product of a grain protein and a saponin (JP-A-4-169155) and the like.
However, emulsifier containing as a base material a protein prepared in accordance with the above-described processes are not always satisfactory from the viewpoints of storage stability under acid conditions or in the presence of a salt, and emulsifying stability such as stability to heating.
Both saponin and bile acid are known as natural surfactants. However, when they are used alone, materials emulsified by them are limited because of their high hydrophilic property. In addition, since a saponin and a bile acid have tastes and odors peculiar to them, they are not desirable as food surfactants.
Accordingly, there is a demand for the development of an emulsifier, particularly a food emulsifier, which has excellent emulsion stability and uses a protein as a base material.
On the other hand, a bread preparing process by using a machine such as a divider and an automatic encrusting machine is accompanied with the drawback that a dough is damaged upon mechanical treatment. In addition, bread obtained by baking up a dough after freezing or cold storage is accompanied with the drawback that it is inferior in a specific volume, internal phase, appearance and quality such as taste, particularly specific volume, to bread obtained by a conventional bread preparing process.
As a process for improving the quality of the bread obtained by baking up a dough after mechanical treatment or freezing or cold storage, known is a process of adding to the dough a dough improver, for example, an emulsifier such as glycerin fatty acid ester (JP-A-61-234733), an enzyme such as amylase or lypase (JP-9-135656), starch (JP-A-62-104536) or gluten (EP-B-134658).
Even if the above processes are used as, it is difficult to overcome the deterioration in the quality of bread as a result of the mechanical treatment or cold or frozen storage. Development of a dough improver for improving bread quality is therefore always desired. Also, in the ordinary bread preparing process, development of a dough improver for further improving the bread quality is desired.